1. Field of the Invention
The present invention relates to a trapping protector for detecting the presence of an object in a sensing region. Said trapping protector comprises a body portion, at least one ground electrode and at least one sensor electrode which is arranged spaced apart from said ground electrode and embedded in said body portion. Additionally, the present invention relates to a system for controlling a power-driven window, comprising said trapping protector and a device for creating input signals to be applied to said sensor electrode and for receiving output signals from said sensor electrode.
2. Description of Related Art
The number of vehicles equipped with a power-driven window or sunroof is increasing, which utilizes the driving force of a motor whereby a light touch to an operating switch permits easy opening and closing of the window or sunroof. However, there exists the danger that foreign matter or a body part may be caught between the upper edge of the window and the window frame upon closing, thus leading to injuries.
National Highway Traffic Safety Administration Standard 118 contains regulations to assure safe operation of power windows.
Several approaches have been made in order to avoid such injuries. U.S. Pat. No. 5,459,962 discloses a trapping protector comprising two mutually spaced apart electrical conductors initiating a switching process of a drive unit when brought in contact. U.S. Pat. Nos. 5,754,017, 5,932,931 and 6,966,071 teach a power-driven window comprising a load detecting means for detecting the drive load of the motor driving the window. Said trapping protectors require physical contact and cause significant squeezing of a body part caught between the upper edge of the window and the window frame. Amended Standard 118 states that the maximum force allowable during closure is to be less than 100 Newton onto a solid cylinder having a diameter of between four and 200 millimeters.
There have been proposed trapping protectors which do not require physical contact and, accordingly, do not cause squeezing. U.S. Pat. Nos. 4,453,112 and 5,621,290, the disclosure of which is incorporated by reference, teach capacitive sensors. Arranged on a window frame is at least one sensor electrode to which an alternating current is applied. As soon as an electrically conductive medium such as a human body part is near said sensor electrode the capacity between said sensor electrode and a ground electrode changes. The change in capacity changes the frequency of an output signal of the sensor electrode. Said change is compared to a reference level, and the motor for the window is stopped or reversed if the change exceeds the threshold. Said capacitive sensors can only detect dielectric materials. Wood, plastic or any other non-conductive material cannot be detected as they do not cause a change of capacity.
It is therefore an object of the invention to provide a trapping protector which is capable of detecting electrically conductive objects without physical contact with said objects and at the same time capable of detecting objects of non-conductive material.
It is a further object of the invention to provide a trapping protector capable of detecting objects of electrically non-conductive material with only minimal squeezing of said objects.
It is another object of the invention to provide a system for controlling a power-driven window which avoids injuries during closure of said window.
The present invention provides a trapping protector wherein the sensor electrode and the ground electrode are arranged spaced apart from each other with a zone of reduced rigidity between said two electrodes. Said zone or xe2x80x9csoft spotxe2x80x9d allows easy displacement of the electrodes with respect to each other.
The present invention further provides a system for controlling a power-driven window comprising a trapping protector as set forth above and a device for creating input signals to be applied to said sensor electrode and for receiving output signals from said sensor electrode.
Said output signals are then processed in order to detect any obstacle between the window and a window frame.
Both the trapping protection and the system in accordance with the present invention may be used especially for vehicle doors. The window frame may either be attached to the door or to the vehicle body.
Any object of dielectric material entering the sensing region will be detected without physical contact due to a change in capacity between said sensor electrode and said ground electrode. The capacity will rise upon presence of said object in the sensing region. Upon detection, a motor driving the window will be stopped or reversed. Any object of non-conductive material will not cause a change of capacity and, accordingly, the motor will not stop. Therefore, the object will be forced in contact with the body portion of the trapping protector, causing displacement of the two electrodes with respect to each other. Said displacement can be effected with minimal force and minimal squeezing due to the soft spot arranged between said electrodes. Displacement of the electrodes with respect to each other leads to a change in capacity which is detected and causes the motor to stop or reverse.
The soft spot may be configured as an air gap or hollow chamber or as material of higher resilience than the body portion, preferably sponge rubber. Both an air gap and a sponge rubber may be coextruded together with the body portion, allowing for easy and simple manufacturing. The sensor electrode may be embedded in the body portion close to said soft spot.
In a first embodiment, the ground electrode is arranged separately from the body portion, preferably as part of a window frame. The body portion may then be attached to the ground electrode. Preferably, the body portion is then configured as a sealing profile for a power window. As only the sensor electrode is embedded in the body portion, said body portion may feature a small cross-section and will not obstruct viewing out of the window. Alternatively, the ground electrode may be embedded in the body portion allowing for easier assembly.
The size and orientation of the sensing region may be changed by suitable shaping and/or arranging of the sensor electrode and the ground electrode with respect to each other, by changing the number of the sensor electrodes and/or of the ground electrodes or by charging the sensor electrode and/or the ground electrode to different potentials.
The body portion of the trapping protector is preferably at least partially made of an electrically non-conductive material in order to insulate the sensor electrode with respect to the ground electrode. However, the body portion may comprise one or several electrically conductive regions. Said regions surround the sensor electrode and/or the ground electrode, thus enlarging their cross-section and changing their shape. The enlarged cross-section provides a higher sensitivity, while the change in electrode shape allows the change in size and orientation of the sensing region. The electrically conductive regions may be provided in a accordance with the pending U.S. application Ser. No. 09/315,795, corresponding to WO 98/25780, the disclosure of which is incorporated by reference.
Several methods may be used in order to detect an object in the sensing region. It is currently preferred to apply random burst signals to the sensor electrode charging it to a fixed potential. Next, the charge of the sensor electrode is transferred to a charge detector comprising a known capacitor. The capacitance of the sensor electrode can then be readily ascertained. The value obtained is compared to a given reference level, and the motor for the power-driven window is stopped or reversed depending on the results of the comparison. Sampling time and sampling period as well as the frequency of the applied signals can be varied. However, it is also possible to use a method as described in U.S. Pat. No. 4,453,112 or U.S. Pat. No. 5,621,290.